Processes for alkylating a variety of aromatic compounds by contacting such compounds with a hydrocarbon radical providing source such as an olefin or alcohol with an alkylatable aromatic compound are widely known. Typically, alkylatable aromatic compounds have included mononuclear aromatic compounds themselves or aromatic compounds containing polar substituents such as a hydroxyl, an amino, an alkoxy, a halogen group and so forth. The catalysts utilized in the alkylation reactions have been acidic; e.g., Lewis acids and used as Friedel-Crafts catalyst systems.
To facilitate an understanding of the scope of alkylation of aromatic compounds including the types of aromatic compounds which are alkylatable and the catalyst systems, reference is made to the following patents:
U.S. Pat. No. 2,115,884 discloses the alkylation of aromatic hydrocarbons such as benzene and napthalene, as well as their halogen, nitro, carboxylic acid, and amine derivatives. The alkylation is effected by contacting the aromatic compound with an olefin while using a hydrated silica or bleaching earth as a catalyst. Temperatures of about 140.degree.-260.degree. C. are used.
U.S. Pat. Nos. 3,733,365; 2,923,745; and 3,701,811 disclose the alkylation of hydroxy aromatics, e.g. phenol, by contacting the aromatic compound with an olefin or alcohol. The catalyst systems utilized in these alkylation processes include polymeric aluminum alcoholates, active alumina activated with an aluminum alcoholate, aluminum halides and metal oxides such as cerium oxide or uranium oxide disposed upon inert carriers such as gamma-alumina, silicon carbide, silica and natural clays, molecular sieves and alumino-silicates.
The ring-alkylation of aromatic amines has generated considerable interest because the aromatic monoamines are valuable intermediates in the manufacture of herbicides, dyestuffs, auxiliaries for rubber and plastics and for textiles. Alkylated diamines have many of the same uses that the mono aromatic amines have, but they may also be used as cross linkers for producing a variety of polyurethanes. The alkylated aromatic amines, particularly toluenediamine, when alkylated have a lower reactivity than the parent aromatic amine and this permits manufacturers to form a variety of molded products in a way that could not be formed earlier. Reaction injection molding (RIM) is one of these processes which lends itself to the use of ring-alkylated aromatic diamines as chain extenders for polyurethanes.
Early processes for the ring-alkylation of aromatic amines resulted from the reaction of aniline hydrochloride with alcohols. Similar results were obtained when an N-alkylanilinium halide was heated and caused to rearrange to the ring alkylated product. This work was done by Hofmann and Martius.
Reilly and Hickenbottom, published in a series of articles, one appearing in J. Chem. Soc., 117, 103, (1920) that nuclear alkylation of amines could be effected by heating an N-alkylaniline with a Lewis acid, such as, zinc chloride.
U.S. Pat. Nos. 3,649,693; and 3,923,892 disclose the preparation of ring-alkylated aromatic amines where the alkyl group is ortho to the amine. The U.S. Pat. No. '693 discloses ring alkylation by reacting an aromatic amine with an olefin in the presence of aluminum anilide. The U.S. Pat. No. '892 shows the alkylation in the presence of an alkyl aluminum halide such as diethyl aluminum chloride. The U.S. Pat. No. '892 shows the alkylation reaction in the presence of aluminum anilide.
Stroh et al in U.S. Pat. No. 3,275,690; 2,762,845; West German AS No. 1,051,271 and Japanese No. 38-4569 disclose various processes for the manufacture of alkylated aromatic amines by effecting reaction between an aromatic amine and an olefin. Representative aromatic amines for alkylation include primary amines, such as, aniline, toluidines, xylidines; secondary amines such as diphenylamine and diamines such as m-phenylenediamine and various toluenediamine isomers. In the U.S. Pat. No. '690, various Friedel-Crafts catalysts such as aluminum chloride, zinc chloride, boron fluoride and other halogen compounds are combined with aluminum to effect the catalytic reaction. In the U.S. Pat. No. '845, aluminum powder is used as a component of the catalyst system. The West German No. '271 uses various bleaching earths and montmorillonite as the catalyst.
Most of the above processes utilize homogeneous catalysis. However, the heterogeneous catalysis of the alkylation of aromatic amines is shown in U.S. Pat. No. 2,115,884; British patent No. 846,226; U.S. Pat. Nos. 4,351,958 and 4,446,329. The U.S. Pat. No. '884 discloses the ring alkylation of aromatic hydrocarbons using activated hydrosilicates and hydrated silicic acids, commonly referred to as bleaching earth. The U.S. Pat. No. '958 discloses the use of iron oxide as a catalyst for such alkylation and the U.S. Pat. No. '329 discloses the use of a metal cation salt of a perfluorosulfonic acid polymer, the polymer typically being sold under the trademark Nafion.
Japanese Patent No. 59-167545 discloses the reaction of N-isopropyl-3-methylaniline in the presence of propylene and a Friedel-Crafts catalyst. The 3-methyl-4-isopropylaniline derivative is produced.
One of the problems associated with the ring-alkylation of aromatic amines with an olefin, even though such processes are alleged to be effective for ortho-alkylation or para-alkylation, is that a large amount of N-alkylated aromatic amine is produced. The N-alkylated product formed in amounts from 2-45% by weight of reactant must be converted to a ring-alkylated product in order for the overall process to have any industrial success. A second problem associated with the ring-alkylation of N-alkylated aromatic amines is that the N-alkylated aromatic amine readily rearranges in the presence of the catalyst to the para-isomer. Under alkylation conditions, particularly at high conversions, e.g., greater than 20%, the amount of para-isomer formed is quite high in relation to the amount of ortho-isomer. Typically, the ortho-para isomer ratio is less than 3:1 and generally less than 1:1. Some other problems described herein regarding the synthesis of ortho-alkylated amine products and those problems associated with the production of N-alkylated aromatic amines are well-illustrated in U.S. Pat. No. 4,351,958, Column 1, lines 32-67, and Column 2, lines 1-34.